US7277477B1 - Zero overhead back channel for adaptive transmit filter updates in SerDes transceivers - Google Patents
Zero overhead back channel for adaptive transmit filter updates in SerDes transceivers Download PDFInfo
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- US7277477B1 US7277477B1 US10/178,662 US17866202A US7277477B1 US 7277477 B1 US7277477 B1 US 7277477B1 US 17866202 A US17866202 A US 17866202A US 7277477 B1 US7277477 B1 US 7277477B1
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- serial
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
- H04L25/40—Transmitting circuits; Receiving circuits
- H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
- H04L25/497—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems by correlative coding, e.g. partial response coding or echo modulation coding transmitters and receivers for partial response systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03343—Arrangements at the transmitter end
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
- H04L2025/03356—Baseband transmission
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L2025/03777—Arrangements for removing intersymbol interference characterised by the signalling
- H04L2025/03802—Signalling on the reverse channel
- H04L2025/03808—Transmission of equaliser coefficients
Definitions
- SerDes transceivers signaling at rates on the order of 3.125 Gbps through typical FR4 back-plane channels utilize a simple 2-tap FIR (finite impulse response) transmit filter to equalize frequency dependent channel loss.
- One of the tap values is adjustable with respect to the other. This scheme is often referred to as pre-emphasis. Since there is only one tap value to adjust, it is left to the user to choose the right value for a given channel.
- a simple 2-tap FIR filter is not sufficient to equalize for high frequency channel loss.
- Proposed solutions include an N-tap FIR transmit filter plus a fixed high boost filter at the receiver. For N>3 it becomes difficult for the user to select appropriate values of each filter coefficient for every channel used by the transceiver, hence, adaptive equalization is utilized. Since the N-tap FIR filter is implemented in the transmitter, the receiver must relay information on tap value updates back to the transmitter in order for the FIR filter to adapt to the channel.
- Some solutions require insertion of additional data on a back channel to indicate tap update information, which results in a small increase in the channel data rate.
- additional versions of control codes utilized in a serial back channel are inserted into the back channel by the receiver to encode adjustments to a pre-emphasis filter in the transmitter. No additional bandwidth in the back channel is used for communicating the adjustment data.
- an additional version of the control code is utilized to encode an adjustment to a specific tap value in a transmit-side filter used for pre-emphasis.
- START_PACKET control codes are utilized to control parameter value adjustments.
- the receiver includes a signal analyzer circuit for determining the magnitude of required tap value adjustments.
- the signal analyzer circuit controls an encoder which inserts additional versions of control codes encoding the parameter value adjustment.
- the transmitter includes a decoder that detects the additional control code versions encoding a tap adjustment and adjusts the parameter value in response thereto.
- the transmit-side filter is an FIR filter having adjustable tap values.
- FIG. 1 is a block diagram of a system utilized in an embodiment of the invention.
- FIGS. 2A and 2B are flow charts illustrating the operation of an embodiment of the invention.
- the data transmitted across SerDes channels is encoded, often using a block code, e.g., the 8B/10B code. Even if a block code is not used to encode the data, delimiters (control characters) mark boundaries of a set of data such as a packet.
- a control codeword START_PACKET may indicate that the following data comprises a packet until the control codeword END_PACKET is sent.
- the transmitter may send the IDLE control code until the next START_PACKET is sent.
- START_PACKET control code versions can be utilized with each one indicating the start of a packet.
- N-tap FIR filter there are N ⁇ 1 adjustable taps. If 2 ⁇ (N ⁇ 1) additional control code versions indicating START_PACKET are available on the back channel, then the N-tap transmit FIR filter can be provided with tap update information without any overhead.
- each of the tap weights can be updated using the following technique.
- START_PACKET_ 0 When START_PACKET_ 0 is observed on the back channel, it indicates the start of a packet on that channel and it encodes that there is no updating of the forward channel FIR filter coefficients.
- START_PACKET_ 1 When START_PACKET_ 1 is observed on the back channel it indicates the start of a packet on that channel and it encodes that the first adjustable tap of the forward channel FIR filter is to be incremented by a step.
- START_PACKET_ 2 When START_PACKET_ 2 is observed on the back channel it indicates the start of a packet on that channel and it encodes that the first adjustable tap of the forward channel FIR filter is to be decremented by a step.
- START_PACKET_ 3 and START_PACKET_ 4 are used to adjust the second adjustable tap weight;
- START_PACKET_ 5 and START_PACKET_ 6 adjust the third adjustable tap weight;
- START_PACKET_ 7 and START_PACKET_ 8 adjust the fourth adjustable tap weight;
- START_PACKET_ 9 and START_PACKET_ 10 adjust the fifth and last adjustable tap weight.
- FIG. 1 depicts Transceivers A and B coupled by a first serial channel 102 for transmitting serial data from the Transceiver A to Transceiver B and by a second serial channel 104 for transmitting serial data from Transceiver B to Transceiver A.
- each transceiver has a transmit and receive channel, in this example, the transmit channel for Transceiver A is the first serial channel 102 and the receive channel is the second serial channel 104 .
- FIG. 1 is a high level block diagram that depicts functional blocks which may be implemented in various forms including processor units, ASICs (Application Specific Integrated Circuits), and various combinations of hardware and software. The blocks of FIG. 1 symbolically represent the functionality of any of the implementations.
- Each transceiver includes a transmit and receive portions.
- the transmit portion includes an encoder block 108 and an FIR block 110 .
- the encoder block 108 receives and serializes data and inserts control codes into a serial transmit channel.
- the FIR filter block 110 includes an adjustment input and performs pre-emphasis on the serial transmit channel prior to transmission.
- the receive portion includes a signal analyzer block 120 and a decoder block 122 .
- the signal analyzer block 120 and decoder block 122 are coupled to the receive data on the receive channel.
- the decoder block 122 utilizes the control codes to recover byte boundaries and to convert the received serial channel to parallel data.
- each transceiver are coupled by an interconnect 130 so that signals may be communicated between the blocks.
- the first serial channel 102 is the back channel for updates to the FIR in Transceiver B and the second serial channel 104 is the back channel for updates to the FIR in Transceiver A.
- the adjustment of the FIR of Transceiver A will be now described.
- the first serial channel 102 is forward channel and the second serial channel 104 is the back channel.
- the signal is analyzed by the signal analyzer 120 to determine whether any tap values of the FIR filter 110 of Transceiver A need to be adjusted. If an adjustment is required, the number of the tap to be adjusted, the direction of adjustment, i.e., increase or decrease the tap value, and the number of adjustment steps are output on a compensation control signal sent to the Transceiver B encoder 108 .
- the Transceiver B encoder 108 inserts the appropriate additional START_PACKET control code, instead of the standard START_PACKET code, to encode the number of the tap to be adjusted and the direction of adjustment. For example, in the encoding scheme described above, if the third tap value were to be increased by three steps then the control code START_PACKET_ 5 would be inserted into the back channel three times in place of the standard START_PACKET code.
- the serial back channel is transmitted over the second serial link 104 with the additional control codes and received by the Transceiver A decoder 122 .
- the START_PACKET_ 5 code is detected at the Transceiver A decoder 112 an adjustment control signal is output to the Transceiver A FIR filter 110 to increase the tap value of the third tap by one unit.
- the above embodiment utilizes a transmit-side, multi-tap FIR filter for pre-emphasis.
- Other embodiments of the invention utilize different types of filters, well-know in the art, which have adjustable parameters such as digital filters of type FIR, digital filters of type IIR (infinite impulse response), and analog filters with a finite number of poles and zeros.
- adjustable parameters such as digital filters of type FIR, digital filters of type IIR (infinite impulse response), and analog filters with a finite number of poles and zeros.
- the technique described above of adaptively providing adjustment information through the insertion of alternate control codes is utilized to communicate the adjustments to be applied to the transmit-side filter.
Abstract
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US10/178,662 US7277477B1 (en) | 2002-06-21 | 2002-06-21 | Zero overhead back channel for adaptive transmit filter updates in SerDes transceivers |
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Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20060050726A1 (en) * | 2004-09-03 | 2006-03-09 | Ahmed Ali U | Transmit adaptive equalization for communication system with one or more serial data channels |
US20060067387A1 (en) * | 2004-09-30 | 2006-03-30 | Ahmed Ali U | Transmit adaptive equalization using ordered sets |
US20090161747A1 (en) * | 2007-12-21 | 2009-06-25 | Agere Systems Inc. | Noise prediction-based signal detection and cross-talk mitigation |
US20100208855A1 (en) * | 2009-02-18 | 2010-08-19 | Dawei Huang | System and method of adapting precursor tap coefficient |
US20110019762A1 (en) * | 2009-07-21 | 2011-01-27 | Fuji Xerox Co., Ltd. | Information transmission system, information transmission device, information transmission method, and computer readable medium storing a program for information transmission |
CN102404256A (en) * | 2010-09-15 | 2012-04-04 | 中国人民解放军国防科学技术大学 | Parameter selection method and device of high speed difference branch signal transmission circuit |
US8229303B1 (en) * | 2006-08-07 | 2012-07-24 | Clariphy Communications, Inc. | Reducing pulse narrowing in the transmitter signal that drives a limiting E/O converter for optical fiber channels |
US8767811B2 (en) * | 2012-07-30 | 2014-07-01 | Lsi Corporation | Back channel adaptation using channel pulse response |
US20140314138A1 (en) * | 2013-04-22 | 2014-10-23 | Nvidia Corporation | Back channel adaptation for transmission under peak power constraints |
CN106413191A (en) * | 2016-10-21 | 2017-02-15 | 天津大学 | LED drive circuit with high speed and high conversion efficiency for visible light communication |
US10411923B2 (en) * | 2003-12-17 | 2019-09-10 | Rambus Inc. | High speed signaling system with adaptive transmit pre-emphasis |
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Cited By (21)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US11706061B2 (en) | 2003-12-17 | 2023-07-18 | Rambus Inc. | High speed signaling system with adaptive transmit pre-emphasis |
US11233678B2 (en) | 2003-12-17 | 2022-01-25 | Rambus Inc. | High speed signaling system with adaptive transmit pre-emphasis |
US10771295B2 (en) * | 2003-12-17 | 2020-09-08 | Rambus Inc. | High speed signaling system with adaptive transmit pre-emphasis |
US10411923B2 (en) * | 2003-12-17 | 2019-09-10 | Rambus Inc. | High speed signaling system with adaptive transmit pre-emphasis |
US7443798B2 (en) * | 2004-09-03 | 2008-10-28 | Agere Systems Inc. | Transmit adaptive equalization for communication system with one or more serial data channels |
US20060050726A1 (en) * | 2004-09-03 | 2006-03-09 | Ahmed Ali U | Transmit adaptive equalization for communication system with one or more serial data channels |
US20060067387A1 (en) * | 2004-09-30 | 2006-03-30 | Ahmed Ali U | Transmit adaptive equalization using ordered sets |
US7516226B2 (en) * | 2004-09-30 | 2009-04-07 | Agere Systems Inc. | Transmit adaptive equalization using ordered sets |
US8229303B1 (en) * | 2006-08-07 | 2012-07-24 | Clariphy Communications, Inc. | Reducing pulse narrowing in the transmitter signal that drives a limiting E/O converter for optical fiber channels |
US20090161747A1 (en) * | 2007-12-21 | 2009-06-25 | Agere Systems Inc. | Noise prediction-based signal detection and cross-talk mitigation |
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US20100208855A1 (en) * | 2009-02-18 | 2010-08-19 | Dawei Huang | System and method of adapting precursor tap coefficient |
US8588328B2 (en) * | 2009-07-21 | 2013-11-19 | Fuji Xerox Co., Ltd. | Information transmission system, information transmission device, information transmission method, and computer readable medium storing a program for information transmission |
JP2011029729A (en) * | 2009-07-21 | 2011-02-10 | Fuji Xerox Co Ltd | Information transmission system, information transmitter, and program |
US20110019762A1 (en) * | 2009-07-21 | 2011-01-27 | Fuji Xerox Co., Ltd. | Information transmission system, information transmission device, information transmission method, and computer readable medium storing a program for information transmission |
CN102404256B (en) * | 2010-09-15 | 2015-04-08 | 中国人民解放军国防科学技术大学 | Parameter selection method and device of high speed difference branch signal transmission circuit |
CN102404256A (en) * | 2010-09-15 | 2012-04-04 | 中国人民解放军国防科学技术大学 | Parameter selection method and device of high speed difference branch signal transmission circuit |
US8767811B2 (en) * | 2012-07-30 | 2014-07-01 | Lsi Corporation | Back channel adaptation using channel pulse response |
US20140314138A1 (en) * | 2013-04-22 | 2014-10-23 | Nvidia Corporation | Back channel adaptation for transmission under peak power constraints |
CN106413191A (en) * | 2016-10-21 | 2017-02-15 | 天津大学 | LED drive circuit with high speed and high conversion efficiency for visible light communication |
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